1. Field of the Invention
The present invention relates to a method and an apparatus for driving a sensorless DC motor having a bridge-type inductance detecting circuit, and more particularly, to a method and an apparatus for driving a sensorless DC motor having a bridge-type inductance detecting circuit which detects an inductance based on a relative position of a phase-coil with respect to a magnetic rotor thereby determining a rotor position.
2. Description of the Prior Art
A video cassette recorder (VCR) includes a capstan motor and a head drum motor. Conventionally, in order to drive those motors, it is required to determine the rotor position by using sensors such as a HALL sensor or an optical sensor in such a manner that a phase curve applied to motors can be controlled according to the rotor position. However, the conventional method requires a space for installing sensors. In addition, the sensors are so expensive that the cost of an article is increased.
Recently, a sensorless motor has become widely used for overcoming the above problems.
In the conventional sensorless motor, as disclosed in U.S. Pat. No. 5,235,264, a rotor's commutation is determined by detecting a back electromotive force (BEMF) induced into the phase coil thereby determining the magnetic rotor's position.
The back electromotive force induced into the coil is in proportion to a rotational velocity of the rotor. Therefore, if the rotor is rotated at a lower speed or in a stop-state, detecting the back electromotive force is very difficult. Accordingly, the method using the back electromotive force requires the rotor to rotate over a predetermined speed so as to sufficiently detect the back electromotive force, otherwise, the commutation of the rotor is unstably controlled.